Electromagnetic shield assembly

ABSTRACT

An electromagnetic shield assembly mounted on a substrate. The electromagnetic shield assembly may have an interior surface spaced from the substrate and may bound a hollow chamber over a circuit assembly. The hollow chamber may be filled with a fluid, such as a gas or a liquid. The electromagnetic shield assembly may also have an edge extending along the substrate around the circuit assembly and may include an electromagnetic shield and a conductive assembly. The electromagnetic shield may substantially enclose the hollow chamber bounded by the electromagnetic shield assembly. The conductive assembly may extend along and may be electrically isolated from the electromagnetic shield. The conductive assembly may be conductively coupled to the circuit assembly.

RELATED APPLICATIONS

The present application is a division and continuation-in-partapplication of U.S. patent application Ser. No. 10/882,886, filed onJun. 30, 2004, the complete disclosure of which is hereby incorporatedby reference herein in its entirety and for all purposes.

BACKGROUND

Electronic circuit components may be surrounded by shields, or covers,to suppress dangerous or disruptive electromagnetic (EM) radiationcreated by electronic circuit components at communication frequencies,including radio frequencies. In some environments, electronic componentsmay be enclosed in some form of conductive cover that is connected to acircuit ground. An EM shield may be a solid metal housing or lid shapedto create a chamber enveloping an electronic circuit. EM shields havebeen developed for use in compact electronic environments that includenumerous electronic components on a substrate. In such compactenvironments, the electronic components may be difficult to isolate fromone another using individual encapsulating EM shields. Shields providingsufficient isolation take up space and also interfere with communicationbetween the various shielded electronic circuits. In such compactenvironments there is a need to provide both effective EM shielding andproper inter-circuit communication while maintaining the compact sizethat is desired in an increasing number of electronic devices.

BRIEF SUMMARY OF THE DISCLOSURE

An electromagnetic shield assembly may be mounted on a substrate. Theelectromagnetic shield assembly may have an interior surface spaced fromthe substrate and may bound a hollow chamber over a circuit assembly.The hollow chamber may be filled with a fluid, such as a gas or aliquid. The electromagnetic shield assembly may also have an edgeextending along the substrate around the circuit assembly and mayinclude an electromagnetic shield and a conductive assembly. Theelectromagnetic shield may substantially enclose the hollow chamberbounded by the electromagnetic shield assembly. The conductive assemblymay extend along and may be electrically isolated from theelectromagnetic shield. The conductive assembly may be conductivelycoupled to the circuit assembly.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plan view of a circuit structure including an EM shieldassembly mounted on a substrate.

FIG. 2 is a cross section taken along line 2-2 of FIG. 1.

FIG. 3 is a cross section taken along line 3-3 of FIG. 2.

FIG. 4 is a cross section taken along line 4-4 of FIG. 2 FIGS. 5-7 arepartial cross sections similar to FIG. 2 of other examples of EM shieldassemblies.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

FIGS. 1-4 depict a simplified exemplary circuit structure 8 including anEM shield assembly 10, or cover having various features illustrated in asingle composite embodiment for convenience. These features may havevarious forms, and may be realized in other shield assembliesindividually or in various other combinations. As used herein, an EMshield assembly may house one or more circuit assemblies 12 that mayindividually or in combination form one or more complete circuits, oneor more portions of one or more circuits, one or more combinations ofelements or components of a circuit, or any combination of circuits,circuit portions, and circuit components, and may include shared circuitportions or components.

In this example, then, EM shield assembly 10 may be mounted to asubstrate 14. EM shield assembly 10, also referred to as an enclosure,may include an electromagnetically conductive layer forming an EM shield16 having a top or distal side 20, and intermediate sides 22, such assides 22 a, 22 b, 22 c, and 22 d, forming an enclosed hollow chamber 26.The hollow chamber may be filled with a fluid, such as a gas or aliquid. When filled with highly insulating liquids, reliability of theenclosed circuit may be improved. Examples of such liquid include gammabutyrolactone, N-methyl-2-pyrrolidinone, hydrofluorocarbons orfluorinated hydrocarbons, fluorocarbons, polychlorobiphenyl, transformeroil (in general), mineral oil (of which there are many grades), andsilicone oils. As seen in the cross-section of FIG. 2, the EM shieldassembly may be a laminate, or may be composed of multiple layers.Conductive exterior or outer layer 16 may extend along the entireexterior of the EM shield assembly. Shield 16 may be made of anelectromagnetically (including electrically or magnetically) conductivematerial, such as aluminum, copper or other metal, and may be formed ofa combination of materials, at least one of which is conductive, such asa conductive layer with a non-conductive (dielectric) or semi-conductivematerial. Directly adjacent to the shield 16 may be dielectric layer orbody 17. Dielectric body 17 may be a composite layer further arranged inone or more layers.

The shield 16 may also include one or more openings or cutouts, such ascutout 24, to allow the passage of electric current, such as in the formof signals or power, into or out of the chamber 26 without substantialcompromise to the shielding. While only one cutout is illustrated inthis example it should be appreciated that EM shield 16 may include morethan one cutout and that such cutouts may be located on the top or anyside of shield assembly 10. As will be seen, an electrical conductor 33,shown mounted on substrate 14, may pass through cutout 24 toelectrically connect circuit assembly 12 with other circuit assembliesor components located outside of the EM shield assembly. Conductor 33may be a wire, a microstrip line, or any other configuration capable ofconducting electrical current.

Shield 16 may protect circuit assemblies, such as assembly 12, enclosedin chamber 26 from environmental and electromagnetic influences and/orisolate the enclosed circuit assemblies. While not shown, a shield 16may further include an interior wall that can separate chamber 26 intomore than one sub-chamber that may be capable of isolating two or morecircuit assemblies.

Circuit assembly 12 may include various components. For purposes ofillustration, circuit assembly 12 may include respective circuitelements 30 and 32 connected by a suitable interconnect, such as by abond wire 34. Bond wire 34 may be connected to circuit element 30 byconnection to a terminal 31 positioned on the circuit element. Circuitelement 30 may include a lumped or distributed element, or combinationor network of passive and/or active elements, such as transmissionlines, resistors, capacitors, inductors, and semiconductor devices, andmay be mounted on a circuit chip having a dielectric, semiconductive orconductive substrate. Furthermore, the circuit assembly 12 may includeone or a combination of diodes and transistors in an integrated circuit(IC) or chip, including, for example, a monolithic microwave integratedcircuit (MMIC), application specific integrated circuit (ASIC), or thelike. For purposes of illustration, circuit element 32 may be anelectrical conductor for transmitting a signal or power relative tocircuit element 30.

As seen in FIG. 2, the EM shield 16 may be mounted directly to substrate14 at one or more points. In this example, substrate 14 is conductiveand provides a ground for the shield. Other forms of substrate may beused, such as a dielectric with one or more conductive layers.Accordingly, shield 16 may be directly attached to substrate 14 using aconductive adhesive 36. Conductive adhesives may include conductiveepoxy, conductive pads, solder, brazing material, deformed metal, z-axisconducting elastomer, or any similar conductive or resistive material.Further, there may be one or more types of conductive adhesive used inthe mounting of EM shield assembly 10. It should be noted that shieldside 22 c may not be directly attached to substrate 14 in the area ofcutout 24.

Optionally, EM shield 16 may include one or more electrical groundconnectors (not here shown) for grounding the shield 16 to the localcircuit ground. These ground connectors may be in the form of metalstrips extending from one or more portions of the shield into thesubstrate, into an adjacent EM shield, or to whatever ground connectionis available.

Conductors 32 and 33 may be mounted onto substrate 14 using insulatinglayers 38. The insulating layers may be in the form of an insulatingepoxy or other adhesive, or an insulating pad. These insulating layersisolate the conductors from the conductive substrate. Circuit element 30of circuit assembly 12 may require that it be grounded, in which casethe backside of circuit element 30 may be attached to substrate 14 usingconductive adhesive 36.

Shield assembly 10 may further include a conductive assembly 39supported by a dielectric body 17 relative to shield 16. Conductiveassembly 39 may provide a continuous electrical path 41 through or alongthe shield assembly. Path 41 may have branches, and multiple paths,whether adapted to carry signals or power. Components of the conductiveassembly may extend along a surface of, or be embedded in, dielectricbody 17. Dielectric body 17 may be a single layer of dielectric or acomposite layer formed of a plurality of layers of dielectric, whichlayers may or may not be separated by one or more layers ofnon-dielectric material. In this example, dielectric body 17 includesfirst and second dielectric layers 42 and 46. The first and seconddielectric layers 42 and 46 may be continuous along EM shield 16,extending along the EM shield top 20 and sides 22 a, 22 b, 22 c, and 22d. Dielectric body 17 may also extend only over one or more portions ofshield 16. In some areas, the first and second dielectric layers 42 and46 may merge into one layer, not separated by any non-dielectricmaterial. The second dielectric layer 46 may have an interior or innersurface or face 48 that defines chamber 26. Although dielectric layers42 and 46 are shown extending across the top and down the sides of theEM shield assembly, separate dielectric layers may be used, forinstance, to form the portion of the dielectric body making up thesides.

Conductive assembly 39 may include a conductive strip 44 that may extendthrough or on dielectric body 17. In the configuration shown, theconductive strip 44 is sandwiched between first dielectric layer 42 andsecond dielectric layer 46. Conductive strip 44 may be composed of anysuitable conductive materials including the conductive metals discussedabove.

The EM shield intermediate sides 22 a and 22 c may include one or morevias 50, such as vias 50 a and 50 c, that extend between the first andsecond dielectric layers 42 and 46. The vias may be formed by drilling,etching, or otherwise creating respective elongated via holes 52, suchas holes 52 a and 52 c. Such via holes, or tunnels, may extend betweenthe first and second dielectric layers 42 and 46, or extend through anindividual layer. These via holes may then be coated or partially orcompletely filled with electromagnetically conductive material to formthe vias.

Vias 50 a and 50 c may extend the entire height of sides 22 a and 22 c,as shown. Shield assembly 10 may have a lower edge 54 in contact withsubstrate 14. Vias 50 a and 50 c, accordingly have lower ends orportions positioned near lower edge positions 54 a and 54 c of theshield assembly, and extend up to upper portions in contact withconductive strip 44 at respective intersection points 56 a and 56 c. Thelower ends of the vias may be connected to signal conductors 32 and 33,respectively, by any suitable means, such as the use of conductiveadhesive 36.

Vias 50 a and 50 c may connect with conductive strip 44 to formconductive assembly 39 within the EM shield assembly 10. Conductiveassembly 39 may be capable of being used as part of a circuit. Forexample, conductive layer 33 may be capable of conducting current or asignal used or generated by circuit element 30 of circuit assembly 12.An electrical current may be conducted from circuit element 30, throughterminal 31, bond wire 34, signal conductor 32, via 50 a, conductivestrip 44, via 50 c, and conductor 33. Thus, through conductor 33, asignal or power may flow between circuit assembly 12 and a circuitoutside of shielded chamber 26.

FIGS. 1-4 show an embodiment of an EM shield assembly 10 that includesonly one conductive strip 44 embedded in shield assembly 10, and whichinterfaces with vias 52 a and 52 c at intersection points 56 a and 56 c,respectively. An EM shield assembly 10 may include more than oneconductive strip or conductive assembly, and such strips may further beembedded between more than two isolating dielectric layers or extend ona dielectric layer or body. Similarly, while these figures show viasformed within two sides of the EM shield assembly, such vias may becontained within all or any combination of sides of the shield assembly.Some examples may include one or more conductive strips along sides 22instead of or in addition to vias. Further there may be multiple viasand/or multiple conductive strips within any one side. Other forms orconfigurations for realizing a conductive assembly 39 may be used.

EM shield assembly 10 may include portions of resistive material 60 thatmay be effective in damping undesired electrical propagation withinchamber 26. Shielded enclosures such as chamber 26 may have resonancesat various frequencies that may interfere with the proper operation ofcircuit assembly 12 within the chamber 26. Resistive material 60 maydecrease or provide damping to such resonances, and a layer of resistivematerial 60 may extend along all or part of dielectric layer 46.

Resistive material 60 may be a layer of resistive ink, film, paint,other resistive coating, or a combination thereof. This material may beapplied by silk-screening, stenciling, spraying, squirting, painting,inkjet printing, lithography, offset printing, or any other convenientmethod. Optionally, resistive material 60 may be applied discontinuouslyaccording to a pattern of distribution so as to create multiple areas ofresistive material.

As shown in FIG. 2, interior shield surface 48 may include a firstresistive material area 62 that is uniform and covers a portion of theinterior shield surface along both the top 20 and the side 22 a ofshield 10. This interior surface may also include a second resistivematerial area 64 that covers only a portion of side 22 c. The resistivematerial may be of uniform thickness, or the thickness may vary. Someareas of resistive material may be connected to substrate 14 usingconductive adhesive 36.

An alternative embodiment is shown in FIG. 4. As seen in thiscross-section, the interior shield surface may be covered with aresistive material 60 that is uniformly patterned. Such a pattern 70 mayhave a predetermined ratio of open, insulating areas 66 to covered,resistive material areas 68. This resistive material pattern 70 may beapplied in a sheet or a film that may include a mesh. Such a film may bedefined having an average resistivity of between 10 ohms/square and 1000ohms/square.

Another embodiment is shown in FIG. 5. As seen in the cross-section,resistive material 60 is disposed within second dielectric body 17.Dielectric body 17 may be formed in multiple steps or layers such as byforming first and second dielectric layers 42 and 46. The resistivematerial may be applied to an intermediate surface by silk-screening,stenciling, spraying, squirting, painting, inkjet printing, lithography,offset printing, or any other convenient method. This resistive material60 may be applied discontinuously according to a pattern of distributionso as to create multiple areas of resistive material, such as thepattern shown in FIG. 4. It will be appreciated then that resistivematerial 60 may be entirely on the interior surface of the shieldassembly, entirely within the shield assembly, or partially within theshield assembly and partially on the surface of the shield assembly.

As has been mentioned, the addition of such a layer of resistivematerials may result in damping of resonances and extraneous couplingswithin chamber 26 over a desired range of frequencies. In order toimprove this damping, resistive material 60 may be selected according toresistivity, and the thickness and pattern in which the material may beapplied. Additionally, damping may be improved by properly selecting thedielectric material included in the first and the second dielectriclayers 42 and 46 of shield 20, and the thickness of this dielectricmaterial.

The EM shield assembly 10 may be fabricated from circuit board material,including conductive and dielectric material. Fabrication of the EMshield assembly 10 and/or the substrate 14, or the circuit structure 8including the EM shield assembly 10, substrate 14, and associatedcircuitry, such as circuit assembly 12, can be carried out together withthe items arrayed on panels. The mass fabrication on panels may then befollowed by an operation to singulate the assemblies.

Through such an assembly, there may be multiple circuit assemblies 12within each chamber 26, and there may be multiple chambers 26 withineach EM shield 10. Additionally, a given EM shield assembly may includeor omit resistive material 60 for damping, and may include or omitconductive assemblies 39.

FIG. 5 also shows in dashed lines a conductive element 50 a, in place ofvia 50 a, disposed partially on the interior surface 48 of shieldassembly 10 and partially through dielectric layer 46, The portion ofconductive element 50 a on the interior surface may be applied usingtechniques similar to the techniques used to apply the resistive layer.The portion of the conductive element 50 a passing through dielectriclayer 46 may be in the form of a via. It will be appreciated then, thatthe conductive assembly 39 may be disposed partially or completely on aninterior or exterior surface of the shield assembly, so long as it iselectrically spaced from the electromagnetic shield 16.

Hollow chamber 26 may be filled with or contain gaseous material. Insome examples, one or more gaseous species may evolve from materialssuch as adhesives, inks, and the like, or may be otherwise producedwithin the hollow chamber. In order to maintain integrity of the EMshield assembly, the assembly may include one or more apertures 80 thatextend between the hollow chamber and the outside of the electromagneticshield assembly, as shown in FIGS. 6-7. A membrane 82 may block or coverthe aperture. In some examples, the membrane may permit one or moregaseous species to pass between the hollow chamber and outside of theelectromagnetic shield assembly. Additionally or alternatively, themembrane may prevent liquids from passing between the hollow chamber andoutside the electromagnetic shield assembly.

In FIG. 6, top or distal side 20 and side 22 a each include apertures 80that extend through the electromagnetic shield assembly, includingelectromagnetic shield 16 and dielectric body 17. A membrane 82 may beadhered to interior surface 48, thereby covering the aperture. As shownin dashed lines in FIG. 6, the membrane may optionally be adhered to anexterior surface 84, thereby covering the aperture.

In FIG. 7, top or distal side 20 and side 22 a are formed from a firstdielectric layer 86 and a second dielectric layer 88 that generallysurround or embed at least a portion of membranes 82′ and 82″. Aperture80′ formed in side 22 a includes apertures portions 90 and 92 extendingthrough first and second layers 86 and 88, respectively. As can be seenin FIG. 7, aperture portions 90 and 92 of aperture 80′ are generallyaligned with each other and forming a continuous aperture 80′ extendingbetween the interior and exterior surfaces of the electromagnetic shieldassembly. Membrane 82′ allows the one or more gaseous species to escapedirectly from the hollow chamber through the membrane 82′ extendingthrough aperture 80′.

Optionally, the membrane may extend well beyond the boundaries of one ormore aperture portions, such as illustrated by aperture membrane 82″ inFIG. 7. In some examples, membrane 82″ may extend to one of the surfacesof the electromagnetic shield assemblies, such as exterior surface 84.In these examples, one or more gaseous species may enter the membrane ataperture portion 90′ and may travel within the membrane to an exposedportion 94, where the one or more gaseous species are emitted.

In other examples, a second aperture portion 92′ may be disposedproximal to, but be partially or completely misaligned or offset fromfirst aperture portion 90′. In examples in which both aperture portions90′ and 92′ exist and are completely offset (no portion of one apertureis aligned between the faces of the electromagnetic shield assembly),such as shown in FIG. 7, one or more gaseous species may enter themembrane at first aperture portion 90′, migrate from one apertureportion to the other through the membrane, and enter the other apertureportion.

In other examples, an aperture may extend only partially through theelectromagnetic shield assembly, such as from one surface to themembrane. Hence, in some examples only aperture portion 90′ or apertureportion 92′ may exist, but not both, and the membrane extends to asurface of the electromagnetic shield assembly.

Membrane 82 may be formed from any appropriate gas permeable and/orliquid repellant material, such as porous polymer and/or fluoropolymerfilms, such as polytetraflouroethylene (ePTFE) sold under theproprietary name GORE-TEX® by W. L. Gore & Associates of Newark,Delaware, metal foils such as palladium foil, and the like. The membranemay permit all gaseous species to pass equally, or may permit somegaseous species, for example species with small molecules such ashydrogen gas, etc., to pass more readily than those with largermolecules such as water vapor. In some examples, the membrane may beconductive, or may include a conductive portion that is coupled to EMshield 16 or to the conductive assembly.

Optionally, a plug (not shown) including a membrane may be removablyinserted into the aperture by threads or a similar retention mechanism.For example, it is known that plugs having such gas permeable materialscovering a channel through the plug are used in the housings for outdoorunits containing microwave radios to allow ventilation of the housingwithout admitting rain or atmospheric contaminants. Membrane vent plugsof this type are available from W. L. Gore & Associates.

Accordingly, while embodiments of circuit structures have beenparticularly shown and described with reference to the foregoingdisclosure, many variations may be made therein. Other combinations andsub-combinations of features, functions, elements and/or properties maybe used. Such variations, whether they are directed to differentcombinations or directed to the same combinations, whether different,broader, narrower or equal in scope, are also regarded as includedwithin the subject matter of the present disclosure. The foregoingembodiments are illustrative, and no single feature or element isessential to all possible combinations that may be claimed in this orlater applications. The claims, accordingly, define inventions disclosedin the foregoing disclosure. Where the claims recite “a” or “a first”element or the equivalent thereof, such claims include one or more suchelements, neither requiring nor excluding two or more such elements.Further, ordinal indicators, such as first, second or third, foridentified elements are used to distinguish between the elements, and donot indicate a required or limited number of such elements, and do notindicate a particular position or order of such elements unlessotherwise specifically stated.

1. A circuit structure comprising: a substrate; a circuit assemblymounted on the substrate; an electromagnetic shield assembly mounted onthe substrate and having an interior surface spaced from the substrateand bounding a hollow chamber over the circuit assembly, theelectromagnetic shield assembly having an edge extending along thesubstrate around the circuit assembly, the electromagnetic shieldassembly including an electromagnetic shield and a conductive assembly,the electromagnetic shield substantially enclosing the hollow chamberbounded by the electromagnetic shield assembly, and the conductiveassembly extending along and electrically isolated from theelectromagnetic shield, the conductive assembly conductively coupled tothe circuit assembly.
 2. The circuit structure of claim 1, in which theelectromagnetic shield forms an outer layer of the electromagneticshield assembly and is formed of an electromagnetically conductivematerial enclosing the conductive assembly.
 3. The circuit structure ofclaim 1, in which the electromagnetic shield has an opening adjacent tothe substrate, and the circuit structure further comprises a conductormounted on the substrate and extending through the opening from outsideof the electromagnetic shield assembly to the conductive assembly forconducting current between the circuit assembly and outside of theelectromagnetic shield assembly.
 4. The circuit structure of claim 1 inwhich the electromagnetic shield assembly includes a dielectric layerseparating the electromagnetic shield and the conductive assembly. 5.The circuit structure of claim 4, in which the conductive assembly isdisposed at least partially within the dielectric layer.
 6. The circuitstructure of claim 5, in which the electromagnetic shield assemblyfurther includes a layer of resistive material.
 7. The circuit structureof claim 6, in which the resistive layer forms at least part of aninterior surface of the electromagnetic shield assembly.
 8. The circuitstructure of claim 6, in which the resistive layer is disposed at leastpartially within the dielectric layer.
 9. The circuit structure of claim6, in which the resistive layer is distributed discontinuously in apattern.
 10. The circuit structure of claim 4, in which theelectromagnetic shield assembly has a distal side opposite from thesubstrate and intermediate sides extending between the distal side andthe substrate, and the dielectric layer extends along the distal sideand at least a first intermediate side of the electromagnetic shieldassembly, the conductive assembly including a conductive strip extendingalong the distal side of the electromagnetic shield assembly, and afirst via extending through the dielectric layer along the firstintermediate side of the electromagnetic shield assembly, the first viabeing connected to the conductive strip, and which, in combination withthe conductive strip, forms a circuit path along the electromagneticshield assembly.
 11. The circuit structure of claim 10, in which thefirst via is also connected to the circuit assembly.
 12. The circuitstructure of claim 11 in which the conductive assembly is disposedbetween the electromagnetic shield and the hollow chamber.
 13. Thecircuit structure of claim 12 further comprising a conductor mounted onthe substrate and extending outside of the electromagnetic shieldassembly, and a second via extending through a second intermediate sideof the electromagnetic shield assembly spaced from the first via, thesecond via connecting the conductive strip to the conductor.
 14. Thecircuit structure of claim 4, in which the electromagnetic shieldassembly includes a resistive material configured to dampen resonancesin the hollow chamber.
 15. The circuit structure of claim 14 in whichthe resistive material is a resistive film.
 16. The circuit structure ofclaim 14 in which the dielectric layer includes an inner surface facingthe hollow chamber and the resistive material is distributeddiscontinuously along the inner surface in a pattern.
 17. The circuitstructure of claim 16, in which the pattern is a uniform pattern havinga predetermined ratio of portions without resistive material andportions with resistive material.
 18. The circuit structure of claim 1,in which the shield includes an opening providing access through theelectromagnetic shield to the conductive assembly, and the circuitstructure further comprises a conductor mounted on the substrate andextending through the opening from outside of the electromagnetic shieldassembly and electrically coupled to the conductive assembly.
 19. Thecircuit structure of claim 1, in which the electromagnetic shieldassembly includes an aperture extending at least partially through theelectromagnetic shield assembly, and the circuit structure furthercomprises a membrane extending across the aperture and adapted to permitone or more gaseous species to pass through the membrane, and therebythe aperture, between the hollow chamber and outside of theelectromagnetic shield assembly, and adapted to prevent liquids frompassing through the membrane.
 20. The circuit structure of claim 19, inwhich the membrane is adhered to an interior surface of theelectromagnetic shield assembly, thereby covering the aperture.
 21. Thecircuit structure of claim 19, in which the membrane is adhered to anexterior surface of the electromagnetic shield assembly, therebycovering the aperture.
 22. The circuit structure of claim 19, in whichthe electromagnetic shield assembly includes a first dielectric layerproximal to the hollow chamber and a second dielectric layer distal tothe hollow chamber, the aperture includes a first aperture portionextending through the first dielectric layer and a second apertureportion extending through the second dielectric, and the membrane isdisposed between the first and second dielectric layers.
 23. The circuitstructure of claim 22, in which the first and second aperture portionsare aligned to form a continuous aperture through the electromagneticshield assembly.
 24. The circuit assembly of claim 22, in which thefirst and second apertures are at least partially misaligned, and themembrane extends between and across both the first and second apertureportions.
 25. The circuit assembly of claim 19, in which the apertureextends only partially through the electromagnetic shield assembly, andthe membrane is disposed within the shield assembly and extendslaterally from the aperture to an exposed surface of the shieldassembly.
 26. The circuit structure of claim 19, in which theelectromagnetic shield assembly has a distal side opposite from thesubstrate, the distal side including the aperture.
 27. The circuitstructure of claim 19, in which the electromagnetic shield assembly hasa distal side opposite from the substrate and intermediate sidesextending between the distal side and the substrate, at least one of theintermediate sides including the aperture.